Electroplating bath for depositing bright zinc plates

ABSTRACT

SEMI-BRIGHT TO FULLY BRIGHT ZINC DEPOSITS ARE PRODUCED BY ELECTROPLATING ARTICLES IN AN ACID ELECTROPLATING BATH CONTAINING A NON-COMPLEX ZINC SALT AND, AS BRIGHTENING AND THE THROWING POWER INCREASING ADDITIVES, AN AROMATIC CARBONYL COMPOUND, A NON-IONOGENIC, SURFACE ACTIVE POLYOXYETHYLENE COMPOUND, AND/OR A COMPOUND SELECTED FROM THE GROUP CONSISTING OF AMMONIUM CHLORIDE AND A COMPOUND FORMING A SOLUBLE COMPLEX COMPOUND WITH ZINC SALTS WITHIN THE PH-RANGE BETWEEN ABOUT 2.5 AND ABOUT 5.5. ELECTROPLATING WITH SUCH BATHS IS PREFERABLY EFFECTED AT A PH BETWEEN ABOUT 2.5 AND ABOUT 5.5, A TEMPERATURE BETWEEN ABOUT 10* C. AND ABOUT 30* C., AND A CURRENT DENSITY BETWEEN ABOUT 1 AMP/SP. DM. AND ABOUT 5 AMP/ SQ. DM. THE BATHS ARE ABLE TO REPLACE THE HERETOFORE USED ALKALINE ELECTROPLATING ZINC BATHS AND ARE SUBSTANTIALLY FREE OF THE DISADVANTAGES OF SAID BATHS, ESPECIALLY THE DIFFICULTIES ENCOUNTERED IN WASTE DISPOSAL.

United States Patent 3,694,330 ELECTROPLATING BATH FOR DEPGSITING BRIGHTZINC PLATES Joachim Korpium, 54 Oherbohringer Strasse, and JoachimSteeg, 47 Schultheiss-Schneider-Strasse, both of 734 Geislingen, GermanyNo Drawing. Filed May 23, 1067, Ser. No. 640,512 Int. Cl. C2311 5/12,5/46 US. Cl. 204-55 R 16 Claims ABSTRACT OF THE DISCLOSURE Semi-brightto fully bright zinc deposits are produced by electroplating articles inan acid electroplating bath containing a non-complex zinc salt and, asbrightening and the throwing power increasing additives, an aromaticcarbonyl compound, a non-ionogenic, surface active polyoxyethylenecompound, and/or a compound selected from the group consisting ofammonium chloride and a compound forming a soluble complex compound withzinc salts within the pH-range between about 2.5 and about 5.5.

Electroplatingwith such baths is preferably effected at a pH betweenabout 2.5 and about 5.5, a temperature between about C. and about 30 C.,and a current density between about 1 amp/sq. dm. and about 5 amp/ sq.dm.

The baths are able to replace the heretofore used alkalineelectroplating zinc baths and are substantially free of thedisadvantages of said baths, especially the difliculties encountered inwaste disposal.

The present invention relates to an acid galvanic electroplating zincsolution or bath and more particularly to an acid zinc bath fordepositing semi-bright or fully bright zinc plates or coatings, to anelectroplating process by means of such an acid zinc bath, and to zinccoated articles obtained by electroplating in such a bath.

Technically useful zinc electrolytes for the hardware industry mustpermit precipitation of bright zinc deposits within a wide range ofcurrent densities. In addition thereto they must have a high throwingpower so that satisfactory zinc deposits are obtained even at recessedareas of the surface to be electroplated. Baths which contain alkalicyanides or alkaline zinc baths which are free of cyanide meet theserequirements in most instances. However, considerable difiiculties areencountered in detoxifying the used electrolyte baths.

Acid zinc baths which operate within the pI-I-range of 2.0 to 6.0, donot cause such difficulties. Drag-outs of the baths into rinsing Waterobtained on electroplating with such acid zinc baths are simplyneutralized and thereby rendered harmless so that they meet the existingregulations. The zinc baths which are known at present, however, arerather unsatisfactory with respect to the brightness of the zincdeposits and their throwing power.

It has been suggested to add aromatic aldehydes together with sulfurousacid or, respectively, sulfites and colloids to solutions of zincsulfate and to use such electrolytes for depositing bright zinc coatingsor plates. Such baths, in fact, yield semi-bright to fully brightdeposits but only within a rather narrow range of current densities.However, said deposits tend to yield pitted zinc coatings or plates. Thethrowing power of such baths is also quite low and corresponds to thatof the acid zinc baths which are known for a long time and which yieldmatte zinc deposits. Therefore, such acid zinc baths have not been usedin the hardware industry.

Thus all attempts to provide acid zinc baths with a satis- I 3,694,330Patented Sept. 26, 1972 factory brightness and throwing power of thezinc precipitation have failed heretofore.

It is now an important object of the present invention to provide anacid electroplating zinc bath which yields not only fully bright Zincdeposits, i.e. plates over a wide range of current densities but thethrowing power of which approximates that of alkaline electroplatingzinc baths.

Another object of the present invention is to provide a simple andeffective electroplating process whereby bright to fully bright zincdeposits are obtained under economic conditions.

Still another object of the present invention are zinc electroplatedarticles of bright appearance which articles are obtained byelectroplating in an acid electroplating bath of a specific compositionto produce bright zinc deposits.

Other objects of the present invention and advantageous features thereofwill become apparent as the description proceeds.

In principle the acid electroplating bath for depositing semi-bright tofully bright Zinc plates according to the present invention comprises anaqueous solution of zinc salts, especially of simple, i.e., not complexinorganic zinc salts and preferably of zinc sulfate, zinc chloride, orzinc fluoborate, Zinc acetate, and others, to which the following agentsare added:

(1) An aromatic carbonyl compound.

(2) A non-ionogenic, surface active polyoxy ethylene compound.

(3) Ammonium chloride and/or a compound capable of forming solublecomplex salts with zinc salts.

Suitable aromatic carbonyl compounds are carboxylic acids, carboxylicacid esters, aldehydes, or ketones, such as benzoic acid, cinnamic acid,salicylic acid, phenyl propiolic acid, benzoyl acetic acid, o-cumaricacid, cinnamic aldehyde, m-hydroxy benzaldehyde, aetophenone,benzophenone, benzoyl acetic acid ethyl ester, and others. Thesecarbonyl compounds are highly efiective when added to the electrolyte inan amount between about 0.1 g./l. and about 20 g./l. Thereby the amountsmay vary within the limits of 225% without any harmful effect.

Useful carbonyl compounds are preferably soluble in water to an amountof 0.1 g./l. Carbonyl compounds of a lower solubility are in general notsufiiciently eflective.

There is a great choice of non-ionogenic, surface active polyoxyethylenecompounds so that a large number of such compounds are available foraddition to the zinc bath. The preferred compounds are those in which atleast six ethylene oxide molecules are condensed with longchain fattyalcohols, long-chain fatty acids, long-chain fatty amines, or long-chainalkyl phenols. The term longchain indicates molecules which contain atleast 6 carbon atoms. Frequently it is advisable to select compoundswith 10 or more oxyethylene groups in the molecule so as to provide goodwater solubility.

The third additive component of the bath composition according to thepresent invention is ammonium chloride and/or a compound capable offorming soluble complex compounds with zinc. The most elfectiveconcentration of ammonium chloride is between about 5 g./l. and about 60g./l. Complex-forming compounds exhibit the desired favorable elfectwhen added in amounts between about 2 g./l. and about 30 g./l. In placeof ammonium chloride, there may be added and used another ammonium saltsuch as ammonium sulfate, ammonium acetate, and others provided asufficient amount of another chloride, such as zinc chloride or sodiumchloride is added to the bath at the same time.

In place of ammonium chloride, there may be used, as stated above,compounds which are capable of forming soluble complex salts with zincions. Such compounds are, for instance, sodium glycerophosphate,triethanolamine, ethylene diamine, or the sodium salt of ethylenediamine tetraacetic acid, and others. Ammonium chloride and thecomplex-forming compounds can readily be exchanged against each other.They can also be used together in the bath.

Although, as will be shown in the examples given hereinafter, thecomplex-forming compounds are added in relatively small amounts, inorder to produce semi-bright to fully bright zinc deposits, it isnecessary, especially if the zinc content of the used baths and rinsingwater must meet very high requirements, to determine by tests whetherthe zinc content of the bath, when it is diluted to the concentration ofthe sewer, can be decreased sufficiently by neutralization to a pH of7.5 to 8.0. While thus the use of complex-forming compounds requirescareful supervision of the used baths and rinsing waters, the zinccontent of waste baths containing ammonium chloride as third componentis always below the admissible limit if the neutralization step isproperly carried out.

The brightness of the zinc deposits, the range of current densitieswithin which semi-bright to fully bright zinc coatings or plates areobtained, and the throwing power of the bath are improved by thecombined use of the three additive components according to the presentinvention to such an extent that such acid zinc baths can successfullybe used for technical electroplating in competition with the heretoforeemployed alkaline bright zinc baths.

Preferably the zinc baths according to the present invention areoperated at a pH between about 2.5 and about 5.5. Higher pH-values maycause precipitation of basic zinc salts. At a lower pH-value the zincanodes are dissolved in the electro without passing currenttherethrough. As a result of such a dissolution of the zinc anode anundesirable increase of the zinc concentration in the bath takes place.

Bright zinc deposits or plates obtained by using electroplating bathsaccording to the present invention can be subjected to a postplatingtreatment whereby they are provided with chromate conversion coatingswhich convert the zinc surface from the naturally occurring oxide to theone containing hexavalent chromium. Chromate conversion coatings may becolorless or may impart various colors to the zinc deposits such asbluish, brown or olive. The brightness of the zinc deposit is evenenhanced especially by colorless or bluish chromate treatment.

The following examples serve to illustrate bright electroplating zincbaths according to the present invention. Semi-bright to fully brightzinc coatings are deposited from such baths at current densities betweenabout 1 amp/sq. dm. and about amp/sq. dm. and a bath temperature betweenabout 15 C. and about 30 C. The baths have a throwing power which isgood enough to employ them for zinc plating of technical articles inplace of alkaline zinc electroplating baths. Even higher currentdensities may be employed when vigorously agitating the electrolyte orthe work.

EXAMPLE 1 One liter of electroplating bath contains 300 g. of zincsulfate,

25 g. of ammonium chloride,

0.6 g. of cinnamic acid, and

3.0 g. of the surface active compound from isononyl alcohol and ethyleneoxide with about 15 (C H O)-groups in its molecule.

pH of the bath: 4.5.

EXAMPLE 2 One liter of electroplating bath contains 225 g. of zincsulfate,

pH of the bath: 5.0.

EXAMPLE 3 One liter of electroplating bath contains 200 g. zinc acetate,

25 g. of ammonium chloride,

0.5 g. of phenyl propiolic acid, and

4 g. of the surface active compound from stearylamine and ethylene oxidewith about 25 (C H O')-groups in its molecule.

pH of the bath: 5.0.

EXAMPLE 4 One liter of electroplating bath contains 250 g. of zincsulfate,

35 g. of ammonium chloride,

0.25 g. of benzal acetone, and

4.5 g. of the surface active compound from tributyl phenol and ethyleneoxide with about 50 (C H O)-groups in its molecule.

pH of the bath: 3.0.

EXAMPLE 5 One liter of electroplating bath contains 325 g. of zincsulfate,

4 g. of ethylene diamine hydrate,

0.15 g. of benzal acetone, and

3 g. of the surface active compound from oleyl alcohol and ethyleneoxide with about 15 (C H O)-groups in its molecule.

pH of the bath: 3.5

EXAMPLE 6 One liter of electroplating bath contains g. of zinc acetate,

40 g. of ammonium chloride,

0.3 g. of benzophenone, and

3 g. of the surface active compound from coconut fatty acids andethylene oxide with about 20 (C H O) groups in its molecule.

pH of the bath: 4.0.

EXAMPLE 7 One liter of electroplating bath contains 350 g. of zincsulfate,

10 g. of sodium glycerophosphate,

0.3 g. of cinnamic aldehyde, and

5 g. of the surface active compound from nonyl phenol and ethylene oxidewith about 15 (C H O)-g,roups in its molecule.

pH of the bath: 4.2.

EXAMPLE 8 One liter of electroplating bath contains 290 g. of zincsulfate,

25 g. of ammonium chloride,

0.25 g. of m-hydroxy benzaldehyde, and

3 g. of the surface active compound from hexanol and ethylene oxide withabout 15 (C H 0)-groups in its molecule.

pH of the bath: 3.7.

EXAMPLE 9 One liter of electroplating bath contains 175 g. of zincsulfate,

30 g. of zinc chloride,

30 g. of ammonium sulfate,

0.4 g. of benzoyl acetic acid ethyl ester, and

g. of the surface active compound from isononyl alcohol and ethyleneoxide with about (C H O)-groups in its molecule.

pH of the bath: 4.5.

EXAMPLE 10 One liter of electroplating bath contains 125 g. of zincchloride,

25 g. of ammonium chloride,

0.5 g. of benzal acetone, and

10 g. of the surface active compound from isononyl alcohol and ethyleneoxide with about 15 (C H O)-groups in its molecule.

EXAMPLE 11 One liter of electroplating bath contains 275 g. of zincsulfate,

10 g. of triethanolamine,

0.6 g. of m-hydroxy benzaldehyde, and

4 g. of the surface active compound from nonyl phenol and ethylene oxidewith about 11 (C H O)-groups in its molecule.

EXAMPLE 12 One liter of electroplating bath contains 220 g. of zincacetate,

16 g. of the disodium salt of ethylene diamine tetraacetic acid,

0.15 g. of benzal acetone, and

3 g. of the surface active compound from oleyl alcohol and ethyleneoxide with about 20 (C H O)-groups in its molecule.

All these electroplating baths yield at the current densities and bathtemperatures as given herein-above fully bright zinc deposits. Thethrowing power of the baths is highly satisfactory.

Of course, many changes and variations in the aromatic carbonylcompound, the non-ionogenic, surface active polyoxyethylene compound,and the compound forming a complex compound with zinc ions, in theamounts of the bath components and additives thereto, in the pH-value ofthe baths, in the current densities and bath temperatures duringelectroplating, and the like may be made by those skilled in the art inaccordance with the principles set forth therein and in the claimsannexed hereto.

We claim:

1. Acid electroplating bath for depositing semi-bright to fully brightzinc plates comprising an aqueous solution, having a pH between about2.5 and about 5.5, of a zinc salt; an aromatic carbonyl compound; anon-ionogenic, surface active polyoxyethylene compound; and a compoundselected from the group consisting of ammonium chloride and thecomplex-forming compounds sodium glycerophosphate, triethanolamine,ethylene diamine, and the sodium salts of ethylene diamine tetraaceticacid; said aromatic carbonyl compound being present in the bath in anamount between about 0.1 g./l. and about 20 g./l.; said non-ionogenic,surface active polyoxyethylene compound being a compound produced bycondensing ethylene oxide with compounds selected from the groupconsisting of long-chain fatty alcohols, long chain fatty acids,long-chain fatty amines, and longchain alkyl phenols, and being presentin the bath in an amount of at least 0.5 g./l.; said ammonium chloridebeing present in the bath in an amount of at least 5 g./ 1.; and theamount of the complex-forming compound in the bath being at least 2g./l.

2. The acid electroplating bath according to claim 1, wherein thenon-ionogenic, surface active polyoxyethylene compound is a condensationproduct of ethylene oxide with a compound selected from the groupconsisting of long-chain fatty alcohols, long-chain fatty acids,long-chain fatty amines, and phenols substituted by a long-chain alkylradical, said condensation product having at least 6 ethylene oxidegroups in its molecule, the long-chain alkyl radical in said fattyalcohols, fatty acids, fatty amines, and alkyl phenols having at least 6carbon atoms.

3. The acid electroplating bath according to claim 2, wherein thecondensation product has at least 10 ethylene oxide groups in itsmolecule.

4. The acid electroplating bath according to claim 1, wherein thesurface active polyoxyethylene compound is present in the bath in anamount between about 0.5 g./l. and about 20 g./l.

5. The acid electroplating bath according to claim 1, wherein ammoniumchloride is present in the bath in an amount between about 5 g./l. andabout 60 g./1.

6. The acid electroplating bath according to claim 1, wherein thecompound forming a soluble complex compound with zinc salts is presentin the bath in an amount between about 2 g./l. and about 30 g./l.

7. The acid electroplating bath according to claim 1, wherein thearomatic carbonyl compound is present in the bath in an amount betweenabout 0.1 g./l. and about 20 g./l., the surface active polyoxyethylenecompound in an amount between about 0.5 g./l. and about 20 g./l., andammonium chloride in an amount between about 5 g./l. and about 60 g./l.

8. The acid electroplating bath according to claim 1, wherein thearomatic carbonyl compound is present in the bath in an amount betweenabout 0.1 g./l. and about 20 g./l., the surface active polyoxyethylenecompound in an amount between about 0.5 g./l. and about 20 g./l., andthe compound forming a soluble complex compound with zinc salts in anamount between about 2 g./l. and about 30 g./l.

9. The acid electroplating bath according to claim 1, wherein thearomatic carbonyl compound is selected from the group consisting of anaromatic carboxylic acid, an aromatic aldehyde, and an aromatic ketone.

10. The acid electroplating bath according to claim 1, wherein the zincsalt is selected from the group consisting of zinc sulfate, zincchloride, zinc acetate, and zinc fluoborate.

11. The acid electroplating bath according to claim 1, wherein the zincsalt is selected from the group consisting of zinc sulfate, zincacetate, and zinc chloride, the aromatic carbonyl compound is selectedfrom the group consisting of cinnamic acid, benzoic acid, phenylpropiolic acid, benzal acetone, benzophenone, cinnamic aldehyde,m-hydroxy benzaldehyde, and benzoyl acetic acid ethyl ester, and thepolyoxy ethylene compound is selected from the group consisting of thecondensation product of ethylene oxide with isononyl alcohol, oleylalcohol, hexanol, coconut fatty acids, stearylamine, nonyl phenol, andtributyl phenol, and the complex forming compound is selected from thegroup consisting of ethylene diamine, triethanolamine, sodiumglycerophosphate, an :l the disodium salt of ethylene diaminetetraacetic aci 12. The acid electroplating bath according to claim 1,wherein said ammonium chloride is formed by addition of equivalentamounts of an anunonium salt other than ammonium chloride and a solublemetal chloride.

13. An acid aqueous zinc electroplating bath having a pH of about 2.5 toabout 5.5, comprising a zinc salt; about 0.1 g./l. to about 20 g./l. ofan aromatic carbonyl compound; at least 0.5 g./l. of a compound selectedfrom the group consisting of condensates of long-chain fatty alcohols,long-chain fatty acids, long-chain fatty amines, and long-chain alkylphenols with ethylene oxide; and a compound selected from the groupconsisting of ammonium chloride and the complex-forming compounds sodiumglycerophosphatc, triethanolamine, ethylene diamine, and the sodiumsalts of ethylene diamine tetraacetic acid; said ammonium chloride beingpresent in the bath in an amount of at least g./-l. and the amount ofthe complex-forming compound in the bath being at least 2 g./l.

14. An acid aqueous zinc electroplating bath having a pH of about 2.5 to5.5, comprising a zinc salt; about 0.1 g./l. to about 20 g./l. of anaromatic aldehyde; at least 0.5 g./1. of a condensate of a long-chainalkyl phenol with ethylene oxide; and at least 5 g./l. of ammoniumchloride.

15. In a process of electroplating articles and depositing thereon abright zinc deposit: the improvement wherein the article iselectroplated as cathode at a pH between about 2.5 and about 5.5 in azinc bath comprising an aqueous solution of a zinc salt; an aromaticcarbonyl compound; a non-ionogenic, surface-active polyoxyethylenecompound; and a compound selected from the group consisting of ammoniumchloride and the complexforming compounds sodium glycerophosphate,triethanolamine, ethylene diamine, and the sodium salts of ethylenediamine tctraacetic acid; said aromatic carbonyl compound being presentin the bath in an amount between about 0.1 g./l. and about 20 g./l.;said non-ionogenic, surface-active polyoxyethylene compound being acompound produced by condensing ethylene oxide with compounds selectedfrom the group consisting of long-chain fatty alcohols, long-chain fattyacids, long-chain fatty amines, and long-chain alkyl phenols, and beingpresent in the bath in an amount of at least 0.5 g./l.; said ammoniumchloride being present in the bath in an amount of at least 5 g./l.; andthe amount of the complex-forming compound in the bath being at least 2g./1.

16. The process according to claim 15, wherein the current density atthe cathode is between about 1 amp/ sq. dm. and about 5 amp/sq. dm., andthe bath temperature is between about 15 C. and about C.

References Cited UNITED STATES PATENTS 2,817,627 12/1957 Ostrow et al.204-44 2,282,252 3/ 1958 Fischer 204- X 2,848,394 8/ 1958 Foulke et a1.204-44 X 3,005,759 10/1961 Safranek et a1. 20455 3,285,840 11/ 1966Lindemann 20455 GERALD L. KAPLAN, Primary Examiner mg UNITED STATESPATENT OFFICE CERTIFICATE OF COECMUN Patent No. 1 3 ,6 94 ,330 DatedSeptember 26 1972 Inventor(s) Joachim Korpiun, Joachim Steeg It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 4: The inventor's name "Korpium" must read Korpiun column3 line 36: "electro" must read electrolyte I Signed and sealed this 8thday May 1973.

attest:

IL.FLETCI-IER ,JB. ROBERT GOTTSCHALK p t't gtin-g Gfiicer Commissionerof Patents

